Embryology and Development Practice Questions

Q: Metanephros develops during which week of embryonic development?

5th week. The development of the human kidney occurs in three successive stages: the **Pronephros**, **Mesonephros**, and **Metanephros**. ### 1. Why the Correct Answer is Right (Option B) The **Metanephros** represents the permanent kidney. It begins its development during the **5th week** of gestation. It originates from two sources: * **Ureteric Bud:** An outgrowth from the mesonephric duct (gives rise to the collecting system). [1] * **Metanephric Blastema:** Derived from the intermediate mesoderm (gives rise to the excretory units/nephrons). Functional urine formation starts around the 10th–12th week. ### 2. Why Other Options are Wrong * **Option A (4th week):** This is the period when the **Pronephros** (rudimentary and non-functional) appears and quickly degenerates. The **Mesonephros** also begins to develop late in the 4th week, serving as a temporary kidney during the first trimester. * **Option C (6th week):** By the 6th week, the metanephros is already undergoing differentiation and begins its **ascent** from the pelvic cavity to the lumbar region. * **Option D:** Incorrect, as the 5th week is the established embryological timeline. ### 3. High-Yield Clinical Pearls for NEET-PG * **Molecular Basis:** The interaction between the Ureteric Bud and Metanephric Blastema is an example of **Reciprocal Induction** (GDNF and RET signaling). * **Ascent of Kidney:** The kidney "ascends" from the pelvis. If it gets trapped under the Inferior Mesenteric Artery (IMA), it results in a **Horseshoe Kidney**. [1] * **Potter Sequence:** Bilateral renal agenesis leads to oligohydramnios, causing pulmonary hypoplasia and limb deformities. * **Ureteric Bud Derivatives:** Ureter, Renal Pelvis, Major/Minor Calyces, and Collecting Tubules. [1]

Q: A male neonate develops small-bowel obstruction due to malrotation of the midgut segment. An x-ray of the abdomen confirms the presence of small-bowel obstruction. The neonate undergoes an emergency laparotomy, untwisting of the malrotated intestines, and partial small-bowel resection for intestinal infarction. Which of the following statements is true of the small intestine (jejunum and ileum)?

It is derived entirely from the midgut.. ### Explanation **1. Why the Correct Answer is Right:** The gastrointestinal tract is embryologically divided into the foregut, midgut, and hindgut based on arterial supply. The **midgut** is supplied by the Superior Mesenteric Artery (SMA) and extends from the distal half of the second part of the duodenum to the junction of the proximal two-thirds and distal one-third of the transverse colon. Therefore, the entire **jejunum and ileum** are derived from the midgut. Malrotation occurs due to the failure of the normal 270° counter-clockwise rotation of this midgut segment around the SMA. **2. Why the Incorrect Options are Wrong:** * **Option B:** The midgut enters the physiologic umbilical hernia during the **6th week** of gestation (not the 5th month). This occurs because the rapidly growing liver and kidneys leave insufficient space in the abdominal cavity. * **Option C:** The intestines return to the abdominal cavity during the **10th week** of gestation. Thus, they remain in the physiologic hernia for approximately **4 weeks**, not 4 months. * **Option D:** The **urachus** is a fibrous remnant of the allantois, connecting the urinary bladder to the umbilicus. The small intestine is attached to the posterior abdominal wall via the mesentery, not the urachus. (The vitelline duct, however, connects the midgut to the yolk sac). **3. Clinical Pearls for NEET-PG:** * **Ladd’s Procedure:** The surgical treatment for malrotation involving detorsion, division of Ladd’s bands, and widening the mesenteric base. * **Ladd’s Bands:** Peritoneal bands crossing the duodenum (causing obstruction) to attach an undescended cecum to the RUQ. * **Radiology:** The "Corkscrew sign" on upper GI contrast studies is diagnostic of midgut volvulus. * **SMA/SMV Relationship:** On ultrasound, a reversal of the normal relationship (SMV located to the left of SMA) is highly suggestive of malrotation.

Q: Endochondral ossification is seen in:

Long bones. **Explanation:** Bone formation (ossification) occurs via two primary mechanisms: **Endochondral** and **Intramembranous** ossification. **1. Why Long Bones are correct:** Endochondral ossification is the process where a **hyaline cartilage model** is first formed and subsequently replaced by bone [1]. This process is characteristic of bones that bear weight and require longitudinal growth, such as the **long bones** of the limbs (femur, humerus, tibia, etc.), the vertebrae, and the pelvis. The growth occurs at the epiphyseal plates until skeletal maturity. **2. Analysis of Incorrect Options:** * **Flat bones of the skull (Option B):** These undergo **intramembranous ossification**, where mesenchymal cells differentiate directly into osteoblasts without a cartilage intermediate [1]. * **Clavicle (Option C) & Mandible (Option D):** These are unique "exceptions." They primarily undergo intramembranous ossification [1]. However, they are often classified as **membrano-cartilaginous** because they possess secondary cartilages (e.g., at the sternal end of the clavicle or the condyle of the mandible). Since the question asks for a definitive example of endochondral ossification, long bones are the most accurate choice. **High-Yield Clinical Pearls for NEET-PG:** * **First bone to ossify:** Clavicle (5th–6th week of intrauterine life). * **Only long bone to ossify in membrane:** Clavicle (mostly). * **Achondroplasia:** A genetic condition specifically affecting **endochondral ossification**, leading to short-limbed dwarfism while the skull (membranous) remains normal-sized. * **Base of the Skull:** Unlike the vault, the bones of the skull base (e.g., ethmoid, sphenoid) ossify endochondrally.

Q: The collecting ducts of the kidney develop from which embryonic structure?

Ureteric bud. The development of the definitive kidney (metanephros) involves a complex interaction between two mesodermal structures: the **Ureteric Bud** and the **Metanephric Blastema**. [1] **1. Why the Ureteric Bud is correct:** The ureteric bud is an outgrowth from the distal end of the mesonephric duct. It undergoes repeated branching to form the **collecting system** of the kidney. This includes the ureter, renal pelvis, major and minor calyces, and approximately 1 to 3 million **collecting ducts**. [1] **2. Why the other options are incorrect:** * **Pronephros:** This is the first, most primitive kidney system. It appears in the cervical region and is non-functional in humans, disappearing completely by the 4th week. * **Mesonephros:** This "interim" kidney functions briefly during the first trimester. While most of it regresses, its duct (Wolffian duct) persists in males to form the reproductive tract (epididymis, vas deferens). * **Metanephros (Metanephric Blastema):** While the metanephros is the definitive kidney, the *blastema* specifically forms the **excretory unit (Nephron)**. This includes Bowman’s capsule, proximal convoluted tubule, Loop of Henle, and distal convoluted tubule. **High-Yield Clinical Pearls for NEET-PG:** * **Reciprocal Induction:** The ureteric bud induces the metanephric blastema to form nephrons; if the bud fails to reach the blastema, **renal agenesis** occurs. * **Polycystic Kidney Disease (Potter’s Theory):** Historically attributed to a failure of fusion between the collecting ducts (ureteric bud) and the nephrons (blastema). * **Duplication of Ureter:** Occurs due to early branching or "double" ureteric buds. [1]

Q: A partial development of the aortopulmonary septum will result in which of the following?

Persistent truncus arteriosus (PTA). The **aortopulmonary (AP) septum** is a spiral-shaped mesenchymal structure derived from **neural crest cells**. Its primary role is to divide the embryonic *truncus arteriosus* into the aorta and the pulmonary artery. **Why Option A is correct:** **Persistent Truncus Arteriosus (PTA)** occurs due to a failure or partial development of the AP septum [1]. When the septum fails to form or fuse completely, the truncus arteriosus remains as a single, large common vessel that receives blood from both the right and left ventricles [1]. This is almost always associated with a Ventricular Septal Defect (VSD). **Why the other options are incorrect:** * **Ebstein’s Anomaly:** This is a congenital malformation of the **tricuspid valve** where the septal and posterior leaflets are displaced downward into the right ventricle. It is not related to septation of the great vessels. * **Transposition of the Great Arteries (TGA):** This occurs due to a failure of the AP septum to **spiral** (it grows straight instead), leading to the aorta arising from the right ventricle and the pulmonary artery from the left. It is a defect in *orientation*, not a failure of *development/formation*. * **Common Ventricle:** This results from the failure of the **interventricular septum** to develop, not the AP septum. **High-Yield Clinical Pearls for NEET-PG:** * **Neural Crest Cells:** These are essential for AP septum formation. DiGeorge Syndrome (22q11 deletion) often presents with PTA due to defective neural crest migration. * **Spiral Septation:** The AP septum must undergo a 180-degree spiral. Failure to spiral leads to TGA. * **Cyanosis:** PTA is one of the "5 Ts" of cyanotic congenital heart diseases (Right-to-Left shunt).

Question 1

Destruction of ovaries prior to the 7th week following fertilization results in what?

Accepted Answer

None of the above

Answer

Pseudohermaphroditism

Answer

Uterine agenesis

Answer

Masculinisation

Question 2

Metanephros develops during which week of embryonic development?

Accepted Answer

5th week

Answer

4th week

Answer

6th week

Answer

None of the above

Question 3

The congenital abnormality of the ileum illustrated below is related to persistence of which of the following structures?

Accepted Answer

Vitellointestinal duct

Answer

Meckel's diverticulum

Answer

Omphalocele

Answer

Gastroschisis

Question 4

A male neonate develops small-bowel obstruction due to malrotation of the midgut segment. An x-ray of the abdomen confirms the presence of small-bowel obstruction. The neonate undergoes an emergency laparotomy, untwisting of the malrotated intestines, and partial small-bowel resection for intestinal infarction. Which of the following statements is true of the small intestine (jejunum and ileum)?

Accepted Answer

It is derived entirely from the midgut.

Answer

In the fetus, it enters the physiologic umbilical hernia in the fifth month.

Answer

It remains in the physiologic hernia for 4 months.

Answer

It is attached to the urachus.

Question 5

A structure marked with a red arrow is derived from which of the following?

Accepted Answer

Endocardial cushion

Answer

Septum primum

Answer

Left venous valve

Answer

Bulbus cordis

Question 6

Neural tube formation occurs when?

Accepted Answer

18 to 23 days post fertilization and is the second stage of craniofacial development

Answer

28 to 38 days post fertilization and is the third stage of craniofacial development

Answer

42 to 55 days post fertilization and is the fourth stage of craniofacial development

Answer

17th day post fertilization and is the first stage of craniofacial development

Question 7

The primitive uteroplacental circulation is functionally established during which period of embryonic/fetal development?

Accepted Answer

End of first month

Answer

First week

Answer

Second week

Answer

Third week

Question 8

Endochondral ossification is seen in:

Accepted Answer

Long bones

Answer

Flat bones of the skull

Answer

Clavicle

Answer

Mandible

Question 9

The collecting ducts of the kidney develop from which embryonic structure?

Accepted Answer

Ureteric bud

Answer

Pronephros

Answer

Mesonephros

Answer

Metanephros

Question 10

A partial development of the aortopulmonary septum will result in which of the following?

Accepted Answer

Persistent truncus arteriosus (PTA)

Answer

Ebstein's anomaly

Answer

Transposition of the great arteries

Answer

Common ventricle

Embryology and Development — MCQs

Embryology and Development — MCQs

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